The present invention relates to the separation of cyclohexanone from mixtures thereof with cyclohexanol and phenol such as are formed by the selective hydrogenation of phenol. It is conventional to subject such mixtures to three successive fractional distillations with the first overheads stream recovered being a cyclohexanone-rich stream containing cyclohexanol at a level between 0.1 and 0.5 percent, the second overheads stream being a mixture of cyclohexanone and cyclohexanol between 50 and 80 percent cyclohexanone and the third overheads stream being a phenol-rich steam containing significant amounts of cyclohexanol and cyclohexanone. Certain high boilers such as cyclohexylcyclohexanone remain in the bottoms in all three distillations and are removed from the system at the bottom of the third column.
Because cyclohexanone is produced in large quantities by hydrogenation of phenol for uses such as caprolactam manufacture, and because such distillations consume substantial amounts of steam or other heat energy for reboiling and require substantial amounts of cooling water for condensing, the possibility of modifying such distillation so as to produce more cyclohexanone for the same steam and cooling water consumption would be a desirable result. Similarly, because such distillations require large and expensive equipment, an increase in the capacity of a series of stills to produce more cyclohexanone would also be desirable. Furthermore, there are many uses for cyclohexanone in which it is desirable to achieve lower levels of cyclohexanol content, while in other uses significantly higher cyclohexanol contents can be tolerated.